Bis oxalato platinate Complexes

Two crystalline modifications of bis(oxalato)platinate(II), Pt(ox)2 (ox = oxalate) have been reported a yellow and a red form. These materials differ in the degree of hydration. The yellow form (240) has been shown to be Ca-[Pt(ox)2](H20)8 and the red modification is Ca[Pt(ox)2](H20)3.5. Unlike the yellow form, the red form (240) has a short Pt-Pt distance of 3.18 A. Thus, the degree of solvation appears critical in this metal-metal bond formation. 

Cation-deficient partial oxidation has been effected on the Pt(ox)2 system. Oxidation of Pt(ox)2 with either nitric acid (380), chlorine (244, 245), dichromate (244, 245), hydrogen peroxide (394), or tetracyanodihaloplatinate-(IV) (244, 245, 273) yields copper colored needless of the Pt(ox)2 ion. Oxygen readily oxidizes aqueous solutions of H2Pt(ox)2 to the violet Hi.64-Pt(ox)2(H20)a (273). Table IX lists a variety of partially oxidized bis (oxalato)-platinate complexes. 

In solution the cation-deficient species exhibit complex (273) pH-dependent equilibria (244, 245), which make purification difficult. Krogmann and Dodel (245) claim that in concentrated aqueous solution a blue-black polymer, (Pt-(ox)2] i , exists in equilibrium, Eq. 50, whereby 

When a high potential field ( 50 V cm ) is applied across crystals of Ki.64Pt(ox)2(H20)a , a color change from bronze to blue-black commences at the anode (167, 259) and propagates along the crystal at a rate proportional to the electric field (167). A similar effect has been abserved for the partially oxidized tetracyanoplatinate system (165, 166, 167, 267,308,395). Concomitantly, the conductivity drops by four orders of magnitude, there is a decrease in pH (of the redissolved crystal), and droplets (pH 7) appear on the cathode (167, 259). These observations have been rationalized as the replacement of protons for potassium ions in the lattices (167), Eq. 52, as well as reduction of the complex, Eq. 53 (167, 259). Consistent with the 

Since partial oxidation of Pt(ox) has been demonstrated, the possibility of partial oxidation of bis(dithioxalato)platinate(II), 7, should be considered. Comparison with an early crystal x-ray measurements has shown that the structures of K2Pt(ox)2(H20)2 and K2Pt(S2C202)2, 7, are not isomorphous (106, 292). Further x-ray, chemical, and physical data is necessary to understand the interrelationships between these species and their chemical and physical properties. Preliminary studies have failed to yield any partially oxidized complexes of 7 (335). 

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